ADE7753ARSZ Analog Devices Inc, ADE7753ARSZ Datasheet - Page 22

• Manufacturer Part Number: ADE7753ARSZ
• Description: IC ENERGY METERING 1PHASE 20SSOP
• Manufacturer: Analog Devices Inc

Specifications of ADE7753ARSZ

• Input Impedance: 390 KOhm
• Measurement Error: 0.1%
• Voltage - I/o High: 2.4V
• Voltage - I/o Low: 0.8V
• Current - Supply: 3mA
• Voltage - Supply: 4.75 V ~ 5.25 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 20-SSOP (0.200", 5.30mm Width)
• Meter Type: Single Phase
• Ic Function: Single-Phase Multifunction Metering IC
• Supply Voltage Range: 4.75V To 5.25V
• Operating Temperature Range: -40°C To +85°C
• Digital Ic Case Style: SSOP
• No. Of Pins: 20
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: EVAL-ADE7753ZEB - BOARD EVALUATION AD7753
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

ADE7753
Antialias Filter
Figure 47 also shows an analog low-pass filter (RC) on the input
to the modulator. This filter is present to prevent aliasing.
Aliasing is an artifact of all sampled systems. Aliasing means
that frequency components in the input signal to the ADC,
which are higher than half the sampling rate of the ADC,
appear in the sampled signal at a frequency below half the
sampling rate. Figure 49 illustrates the effect. Frequency
components (arrows shown in black) above half the sampling
frequency (also know as the Nyquist frequency, i.e., 447 kHz)
are imaged or folded back down below 447 kHz. This happens
with all ADCs regardless of the architecture. In the example
shown, only frequencies near the sampling frequency, i.e.,
894 kHz, move into the band of interest for metering, i.e., 40 Hz
to 2 kHz. This allows the use of a very simple LPF (low-pass
filter) to attenuate high frequency (near 900 kHz) noise, and
prevents distortion in the band of interest. For conventional
current sensors, a simple RC filter (single-pole LPF) with a
corner frequency of 10 kHz produces an attenuation of
approximately 40 dB at 894 kHz—see Figure 49. The 20 dB per
decade attenuation is usually sufficient to eliminate the effects
of aliasing for conventional current sensors. However, for a di/dt
sensor such as a Rogowski coil, the sensor has a 20 dB per
decade gain. This neutralizes the –20 dB per decade attenuation
produced by one simple LPF. Therefore, when using a di/dt
sensor, care should be taken to offset the 20 dB per decade gain.
One simple approach is to cascade two RC filters to produce the
–40 dB per decade attenuation needed.
ADC Transfer Function
The following expression relates the output of the LPF in the
Σ-∆ ADC to the analog input signal level. Both ADCs in the
ADE7753 are designed to produce the same output code for the
same input signal level.
Therefore with a full-scale signal on the input of 0.5 V and an
internal reference of 2.42 V, the ADC output code is nominally
165,151 or 2851Fh. The maximum code from the ADC is
±262,144; this is equivalent to an input signal level of ±0.794 V.
However, for specified performance, it is recommended that the
full-scale input signal level of 0.5 V not be exceeded.
0
Figure 49. ADC and Signal Processing in Channel 1 Outline Dimensions
Code ADC
2
FREQUENCIES
IMAGE
(
) 3.0492
=
FREQUENCY (kHz)
ALIASING EFFECTS
447
×
V
V
OUT
IN
×
262,144
894
FREQUENCY
SAMPLING
02875-0-048
Rev. A | Page 22 of 60
(1)
ADE7753 Reference Circuit
Figure 50 shows a simplified version of the reference output
circuitry. The nominal reference voltage at the REF
2.42 V. This is the reference voltage used for the ADCs in the
ADE7753. However, Channel 1 has three input range selections
that are selected by dividing down the reference value used for
the ADC in Channel 1. The reference value used for Channel 1
is divided down to ½ and ¼ of the nominal value by using an
internal resistor divider, as shown in Figure 50.
The REF
example, an external 2.5 V reference. Note that the nominal
reference value supplied to the ADCs is now 2.5 V, not 2.42 V,
which has the effect of increasing the nominal analog input
signal range by 2.5/2.42 × 100% = 3% or from 0.5 V to 0.5165 V.
The voltage of the ADE7753 reference drifts slightly with
temperature—see the ADE7753 Specifications for the
temperature coefficient specification (in ppm/°C). The value of
the temperature drift varies from part to part. Since the
reference is used for the ADCs in both Channels 1 and 2, any
x% drift in the reference results in 2×% deviation of the meter
accuracy. The reference drift resulting from temperature
changes is usually very small and it is typically much smaller
than the drift of other components on a meter. However, if
guaranteed temperature performance is needed, one needs to
use an external voltage reference. Alternatively, the meter can be
calibrated at multiple temperatures. Real-time compensation
can be achieved easily by using the on-chip temperature sensor.
CHANNEL 1 ADC
Figure 51 shows the ADC and signal processing chain for
Channel 1. In waveform sampling mode, the ADC outputs a
signed twos complement 24-bit data-word at a maximum of
27.9 kSPS (CLKIN/128). With the specified full-scale analog
input signal of 0.5 V (or 0.25 V or 0.125 V—see the Analog
Inputs section) the ADC produces an output code that is
approximately between 0x2851EC (+2,642,412d) and
0xD7AE14 (–2,642,412d)—see Figure 51.
PTAT
IN/OUT
Figure 50. ADE7753 Reference Circuit Output
pin can be overdriven by an external source, for
60µA
2.5V
LOAD = 10µA
MAXIMUM
1.7kΩ
12.5kΩ
12.5kΩ
12.5kΩ
12.5kΩ
REF
2.42V
IN/OUT
OUTPUT
IMPEDANCE
6kΩ
REFERENCE INPUT
TO ADC CHANNEL 1
(RANGE SELECT)
2.42V, 1.21V, 0.6V
IN/OUT
02875-0-049
pin is